The present invention relates to an adapter circuit for adapting a conventional ignition system of an engine to a capacitor discharge ignition system and, in particular, to an adapter circuit assembly which may be used with both existing positive and negative polarity systems.
The well-known advantages of a capacitor discharge ignition (CDI) system often render the conversion of an existing conventional ignition system to a CDI system desirable. Typically, the conventional ignition system comprises a source of electric energy which is controllably connected and disconnected to and from the primary winding of an ignition coil via a controlled conduction element such as a set of breaker points which are actuated at selected operating position(s) of the engine. In U.S. Pat. No. 3,704,397 and in U.S. patent application Ser. No. 315,139, both of which are assigned to the same assignee as the present application, there are disclosed embodiments of ignition adapter circuits for converting existing conventional ignition systems to CDI systems. Certain features of the present disclosure relate to improvements in certain features of the ignition adapter circuits disclosed in the aforementioned patent and application. One of these improvements is that the present invention provides a novel adapter circuit which may be used with both positive and negative polarity existing conventional ignition systems. Accordingly, the present invention has the advantage of reducing the number of unique types of adapter circuits required for accommodating both positive and negative polarity existing ignition systems which are to be converted to CDI systems. The adapter circuit according to the present invention also attains the desired objective of eliminating any need for mechanical revision or modification of existing ignition hardware when being installed. In other words, the adapter circuit of the present invention is installable by simply mounting the adapter on the engine and remarking at most a few simple electrical connections.
Additionally, the particular details of certain structure of the present invention attain marked improvements in operational performance of capacitor discharge ignition systems regardless of whether these ignition systems are original equipment CDI systems or conventional systems which have been converted to CDI. One of these improvements involves a novel triggering circuit which provides hard triggering for a triggerable solid state device through which a main capacitor discharges into the primary winding of the ignition coil. Another improvement is that either positive or negative capacitor voltages can be discharged into the primary winding of the ignition coil. As will be seen in the ensuing detailed description of the preferred embodiment, the circuit construction by which these advantageous features and benefits are attained requires a minimum number of individual circuit elements, and hence the preferred adapter circuit assembly may be manufactured economically and can attain high reliability. Accordingly, the invention is also directed to attaining improved operational performance in capacitor discharge ignition systems in general, and to minimizing the costs of such systems.
The foregoing advantages, benefits and features of the invention along with additional features will be seen in the ensuing description and claims which are to be taken in conjunction with the accompanying drawing.